Shared mesh protection (SMP) is a common protection and recovery mechanism in transport networks, where multiple paths can share the same set of network resources for protection purposes. Shared mesh protection allows paths that do not share common points of failure to share protection resources. This is based on the assumption that the likelihood of simultaneous multiple failures or failures within the repair window is low.
When considering control plane based recovery mechanisms it is possible to provide the necessary communication and coordination between nodes to enact pre-emption in shared mesh networks. However this is a time consuming process and will not produce the sort of recovery times expected of a transport network. Hence a solution is desired that works when executive action has been delegated to the data plane that will operate at protection switching speeds, in the order of milliseconds.
The operation of shared mesh protection has extra caveats of preemption and over-subscription. Handling these issues may be an undesirable message and database intensive issue that the nodes of the network will have to handle. Existing solutions attempt to coordinate path preemption by explicit coordination protocols and in some cases knowledge of the business priority of the set of paths in the shared resource. This has a number of issues:
1) Coordination of many path protection/preemption selectors will slow down the protection switching time for the network.
2) Pre-emption means ALL of a preempted customers traffic is discarded, even if the bandwidth available is not fully consumed by the preferred service.
3) Packet pipes are infinitely elastic and therefore the issue of what paths to preempt in order to support a preferred path becomes a much more complex problem and one that has to be coordinated at all preemption points such that all selectors match up and this imposes constraints on how shared protection domains can be set up. Any attempt to impose a distributed algorithm to allow uncoordinated yet a common decision process requires that the ingress and egress selectors need a common view of the path set in order to independently agree on what to preempt.